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Description of the Business and Summary of Significant Accounting Policies - Deferred Commissions, Net (Details) - USD ($)
 3 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2018
Capitalized Contract Cost [Line Items]      
Additional contract costs deferred $ 7,300,000 $ 9,800,000  
Deferred contract costs, amortization period 5 years    
Amortization of deferred commissions $ 3,900,000 $ 2,400,000  
Impairment loss related to deferred costs 0    
Deferred Commissions | Prepaid Expenses and Other Current Assets      
Capitalized Contract Cost [Line Items]      
Deferred contract costs 15,900,000   $ 14,500,000
Deferred Commissions | Other Assets      
Capitalized Contract Cost [Line Items]      
Deferred contract costs $ 40,300,000   $ 38,300,000